1. Technical Field
The present invention relates to technical fields of an photodetector including, for example, an optical sensor, an electro-optical device including the photodetector, such as a liquid crystal device, and an electronic apparatus including the electro-optical device.
2. Related Art
An example of an electro-optical device includes a liquid crystal device in which liquid crystal is interposed as an electro-optical material between a pair of substrates. In such a liquid crystal device, gray-scale display is performed, for example, by applying a predetermined voltage to liquid crystal for every pixel portion formed in an image display region in a condition where the liquid crystal is in a predetermined aligned state between the pair of substrates that form a liquid crystal panel, so that the alignment or order of liquid crystal can be changed to modulate light.
It is known that the visibility in such a liquid crystal device changes according to the surrounding brightness (for example, light intensity of ambient light). For example, when the vicinity of a liquid crystal device is relatively bright (for example, when ambient light is relatively strong), it improves the visibility to make the brightness (specifically, brightness of light from a backlight) of the liquid crystal device relatively high. On the other hand, for example, when the vicinity of a liquid crystal device is relatively dark (for example, when ambient light is relatively weak), the visibility does not get worse even if the brightness of the liquid crystal device is not bright more than needed. In order to realize such a configuration, JP-A-2007-205902 discloses an optical sensor including a first photodiode to which ambient light or light from a backlight is irradiated and a second photodiode from which only the ambient light is shielded. In the optical sensor, the first photodiode and the second photodiode are connected in series. Accordingly, a difference between an output of the first photodiode and an output of the second photodiode can be output. As a result, it is possible to output a received photocurrent (that is, a received photocurrent based on only ambient light) in which influences of light from the backlight and temperature characteristics of photodiodes themselves (for example, a backlight photocurrent generated when receiving light from the backlight and a heat current changing with the environmental temperature) are eliminated.
Here, in order to detect the light intensity of ambient light with high precision, it is preferable to bring a spectral sensitivity characteristic of a photodiode close to the relative luminosity characteristic that is the sensitivity of human eyes. However, the spectral sensitivity characteristic of a photodiode may be different from the relative luminosity characteristic that is the sensitivity of human eyes. For example, when a PIN diode manufactured by a low temperature poly silicon process is used as the optical sensor, the PIN (P Intrinsic N) diode has sensitivity not only to a visible light component but also to a near-infrared light component (specifically, a light component having a wavelength of about 700 nm to 1200 nm). For this reason, in the optical sensor including the first photodiode to which ambient light or light from the backlight is irradiated and the second photodiode from which only the ambient light is shielded, not only a received photocurrent based on a visible light component of the ambient light but also a received photocurrent based on a near-infrared light component not sensed by human eyes is output from the optical sensor. Accordingly, for example, even in a situation where it is sensed that the surrounding environment (that is, ambient light) is ‘dark’ by human eyes, it is determined that the ambient light is relatively bright as much as the output of the received photocurrent based on the near-infrared light component of the ambient light. As a result, a technical problem that the brightness of a display device cannot be suitably adjusted occurs.